Abrasive wheels are generally formed by bonding together abrasive grains or particles with a bonding material, typically a resin. Such wheels are employed in grinding operations. For example, xe2x80x9cthinxe2x80x9d wheels are used in cutoff and snagging operations and may be used without external cooling. Thin abrasive wheels may have no reinforcement or they may be fabric or filament reinforced. Thin abrasive wheels can have full or partial (zone) reinforcement.
Both flat and depressed center abrasive wheels are available. Flat (Type 1) wheels typically are held between two flanges of equal size and mounted on the rotating spindle of a machine.
Depressed center abrasive wheels are characterized by a displacement of the central portion (or the hub) of the wheel with respect to the periphery of the wheel. One face of the wheel has a depressed central portion, while the other face exhibits a raised center. Classified as Type 27 or Type 28, these wheels can be used for cutting or grinding.
Generally, depressed center wheels are mounted on angle machines between two flanges: a rear flange, facing the raised central portion or the raised hub of the wheel, and a front flange. While the front flange fits entirely within the depressed center, the back flange typically covers the raised center and extends beyond it onto the flat portion of the wheel.
Hub assemblies hold the wheel between the two flanges for mounting it onto the spindle of a grinding machine. Often, a hub assembly has two parts, each generally corresponding to the rear and front flange, and are held together by a threaded nut. In another hub assembly design, the two pieces are bonded to the wheel by using an epoxy resin. A one-piece hub assembly which is integrally molded to the wheel has also been developed. In some cases, the mounting assemblies are sufficiently inexpensive to allow discarding the mounting hub along with the worn-out wheel.
Since abrasive wheels are operated at high rotational speeds and used against hard materials such as steel and other metals, masonry or concrete, they must be capable of withstanding these conditions and of operating safely. Furthermore, since they wear out and need to be replaced, keeping their cost of manufacturing low is also important. Because maximum stress occurs at or near the center of the hub, the hub portion of the wheel usually contains additional reinforcing material, typically one or more circles of fiberglass cloth extending approximately to the juncture of the hub and the grinding face of the wheel. Typically, about one-third of the fiberglass cloth is wasted in cutting these circles.
Therefore, a need exists for safe abrasive wheel assemblies and for lowering their manufacturing costs.
The present invention relates to an abrasive wheel assembly including a wheel having a rear face and a front face. The assembly also includes a rear flange at the rear face of the wheel and a front flange at the front face of the wheel. Between the front face of the wheel and the front flange, there is a reinforcement layer having a polygonal shape such as a hexagon. The largest diameter of the reinforcement layer is no greater than 75% of the outer diameter of the wheel.
The present invention also relates to a depressed center abrasive wheel assembly. The assembly comprises an abrasive wheel having two faces. The rear face includes a raised hub and a flat rear wheel region while the front face includes a depressed center and a flat front wheel region. The assembly further comprises a rear flange covering the raised center and a front flange positioned at the depressed center. Between the front face of the wheel and the front flange, there is a reinforcement layer having the shape of a polygon. The largest diameter of the polygonal reinforcement layer is no greater than 75% of the outer diameter of the wheel.
The present invention is also related to an abrasive wheel assembly comprising a flat wheel which is not internally reinforced and has a rear face and a front face. The assembly also includes a rear flange at the rear face of the wheel and a front flange at the front face of the wheel. Between the front face of the wheel and the front flange, there is a reinforcement layer having the shape of a triangle, square, pentagon, hexagon, octagon or other polygon. The largest diameter of the reinforcement layer is no greater than 75% of the outer diameter of the wheel. In one embodiment, the wheel is a flat wheel.
The present invention is also related to a reinforced abrasive flat wheel assembly comprising a wheel which is internally reinforced and has a rear face and a front face. The assembly also includes a rear flange at the rear face of the wheel and a front flange at the front face of the wheel. Between the front face of the wheel and the front flange, there is a reinforcement layer having the shape of a pentagon, hexagon or octagon. The largest diameter of the reinforcement layer is no greater than 75% of the outer diameter of the wheel.
This invention has several advantages. For example, the reinforcement layer provides additional strength to the wheel assembly. The layer also forms a pad between the front flange and the depressed center of the wheel, thereby minimizing any empty space that might exist between the wheel front face and the front flange. Since the layer is 75% or less of the outer wheel diameter, savings in layer materials are obtained. Also, since the layer is typically cut from cloth, shapes such as, for example, hexagons provide significant reductions in the waste of cloth material, thereby significantly lowering the manufacturing cost of wheel assemblies.